Our goal is to obtain stable multielectrode recordings from spinal cord below a spinal transection in rats and follow the neural changes that occur after spinal cord injury and as a result of rehabilitation processes. To do this we will use multielectrode neural recordings and microstimulation. The data will be unique and novel with major potential impacts on our understanding of spinal cord injury, and possible technology transfer to clinical applications. We will use and further develop novel electrode designs initiated in our laboratory to achieve our objectives. Specific Aim 1 : We will further develop a chronic intraspinal multielectrode probe with recording sites along its length, using novel braided composite electrodes. We will add recording sites distributed along the inserted probe length in order to sample neural activity across laminae. To do this we will add laser ablation techniques to our existing construction. We also plan to reduce component wire diameter by a factor of 2-3 (from current 13 micron wire plus insulation components), increasing wire and probe compliance by a factor of 16 to 81 times beyond current values. Specific Aim 2: We will use our electrodes to record activity patterns in spinal cord throughout the process of robot assisted rehabilitation in T9/10 spinalized (ST) rats (both neonatal and adult ST rat injuries). We hypothesize that robot rehabilitation after SCI causes within session dynamic alterations in neural activity, which persist day to day, and correlate with improving functional recovery and weight support. These experiments will provide completely novel data and insights into the rehabilitation process at spinal levels and new measures for assessing rehabilitation and neuroplasticity. Specific Aim 3: We will perform intraspinal microstimulation tests in T9/10 spinalized rats (both neonatal and adult ST rat injuries), either throughout, or after, robot assisted rehabilitation. Our hypothesis is that differences in microstimulation between the groups early and late in training will correlate to functional recovery and robot training effects. These new stimulation data are also expected to provide a set of novel outcome measures and circuit test tools for assessing the interaction of focal spinal stimulation, rehabilitation and neuroplasticity. This project has the potential to have enormous and possibly transformative impacts on our understanding of spinal cord function, injury, and rehabilitation processes using standard animal models. Further, the technologies being tuned in Aim 1 may have broad applicability in neural recording and stimulation in many brain areas, and thus enable new generations of neural recording tools and neuroprosthetics.